History and physical examination are most important tools for diagnosing diabetes Mellitus, however to confirm diagnosis one should have following laboratory tests.

Urine sugar test
Urine ketones test
OGTT-Oral Glucose Tolerance Test , (also called glucose challenge test)
Blood glucose tests
FPG-Fasting plasma glucose Test
Random plasma glucose Test

Tests for ongoing monitoring of diabetes control: HbA1c blood test - an average blood sugar measure over about 3 months. Fructosamine blood test - an average blood sugar measure over about 2 weeks

It is not necessary that one should have all the tests given in above list, but it is necessary to diagnose your disease if you want best treatment for your illness.

How frequently a person must check his sugar level is the decision of your doctor. It mainly depends upon patients age and number of risk factors like blood pressure, higher cholesterol or smoking. If you are above 45 years then you should have your blood sugar level after every 3 years. Even if you are below 45 years and have one or more risk factors then you should also check your blood sugar level frequently.

A- Urine sample for sugar and Ketones: You may have your urine analysis for sugar or ketones which are produced by breakdown of fat and muscle cells to diagnose diabetes but you should keep in mind that if you are having positive urine test for sugar then it is not necessary that you are suffering from diabetes because there are other conditions as well which also cause sugar to appear in urine.

B-THE FASTING BLOOD GLUCOSE (SUGAR) TEST For diagnosing Diabetes Mellitus one must have this test because it is best, easy and comfortable to perform. You should have overnight fast (at-least 8 hours) before performing this test. If fasting blood glucose is below 100mg/dl, then you don't have diabetes. Between 100mg/dl to 125mg/dl is called a Pre-diabetes or Impaired fasting glucose condition. If fasting blood glucose is above 126mg/dl on more than two occasions then you are suffering from diabetes.

C-RANDOM (NON-FASTING) BLOOD GLUCOSE TEST It is also a good test for diagnosing diabetes. In this test we take sample of blood shortly after taking a meal and then check glucose level in blood. If this level is above 200mg/dl, then there are much chances that you are suffering from diabetes. But diagnosis should be confirmed the very next day by fasting blood glucose or by glucose tolerance test

D-ORAL GLUCOSE TOLERANCE TEST (OGTT): Though this test is not commonly used these days but it is still a gold standard for diagnosing diabetes. For diagnosing gestational diabetes this is best test.

Instructions for OGTT: This is test for a person who is in good health and have no other illness. Person should be normally active and not bed ridden. Person is not taking anti diabetic drugs or any drug which alters blood sugar level. Before test, person should eat high carbohydrate diet for three days. No alcoholic beverages. On test day one should not smoke or take coffee.

Glucose Tolerance Test Procedure: First normal blood glucose is tested. Then person drinks 75gm of glucose, for pregnant woman dose of glucose is 100 gm. Then blood samples are taken at particular intervals for measuring blood glucose level.Blood glucose level is measured five times over a period of 3 hours. In simple words, in normal person, this blood sugar level gets higher value by taking 75gm of glucose, however it falls down quickly, but in person having diabetes the blood sugar level rises higher than normal but does not come down quickly. If a person have fasting blood glucose above 140mg/dl and 2 hours value after 75gm of oral glucose greater than 200mg/dl and considered as diabetics. If 2 hours blood glucose value between 140-200mg/dl is labeled as Pre-diabetic condition or impaired fasting glucose. During pregnancy, 2 hours blood glucose value between 140-200mg/dl is treated as a case of diabetes.

OTHER TESTS Glycosylated haemoglobin Test or HB A1 Test: Very important test which tells you how good you are in controlling your blood sugar. It shows your blood sugar control during the past 2 to 3 months. For normal individuals, a good hemoglobin A-1-c is 7 percent.